Electrophotographic imaging members, or photoreceptors, typically include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the dark so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated.
Many advanced imaging systems are based on the use of small diameter photoreceptor drums. The use of small diameter drums places a premium on photoreceptor life. A major factor limiting photoreceptor life in copiers and printers is wear. The use of small diameter drum photoreceptors exacerbates the wear problem because, for example, three to ten revolutions are required to image a single letter-size page. Multiple revolutions of a small diameter drum photoreceptor to reproduce a single letter-size page can require up to one million cycles from the photoreceptor drum to obtain 100,000 prints, a desirable goal for commercial systems.
For low volume copiers and printers, bias charging rolls (BCR) are desirable because little or no ozone is produced during image cycling. However, the micro corona generated by the BCR during charging damages the photoreceptor, resulting in rapid wear of the imaging surface, e.g., the exposed surface of the charge transport layer. For example, wear rates can be as high as about 16 microns per 100,000 imaging cycles. Similar problems are encountered with bias transfer roll (BTR) systems. One approach to achieving longer photoreceptor drum life is to form a protective overcoat on the imaging surface, e.g. the charge transporting layer of a photoreceptor. This overcoat layer must satisfy many requirements, including transporting holes, resisting image deletion, resisting wear, and avoidance of perturbation of underlying layers during coating.
Robust overcoat layers are being designed for long life photoreceptor application that meet required electrical properties, exhibit improved crack and scratch resistance, deletion resistance, and provide excellent print quality. The robust nature of these overcoat layer designs is primarily attributed to extensive crosslinking catalyzed by a strong acid. Although the strong acid enables short curing times, it reduces solution shelf life and therefore restricts coating production. Previous overcoat layer formulations have used pyridine as a masking agent to inhibit the acid catalyst until the catalytic function is desired. Such formulations have exhibited improved solution shelf life and adequate electrical characteristics. However, pyridine is a highly toxic compound. There remains a need for a masking agent that will extend solution shelf life and exhibit excellent electrical characteristics, while meeting environmental health and safety standards.